It is known that protein fiber products such as wool products cause a so-called hygral expansion phenomenon in which the length of a fiber product expands and contracts depending on difference in water-containing rate even when relaxation shrinkage is completely removed. Resulting from this phenomenon, there has been such an inconvenience that when the temperature and humidity of an atmosphere in which the protein fiber product is placed change, the size of the fiber product is not stabilized, and when the fiber product is woolen fabric, deficiency in quality is caused such as puckering, bubbling, non-uniform sizes and the like.
In the prior art, in order to stabilize the hygral expansion behavior, the fiber product is subjected to a water repellent treatment, the fiber product is subjected to a water repellent treatment followed by a baking treatment, or the fiber product is subjected to a treatment using a thiol derivative followed by an oxidation treatment. However, the stabilization effect on the hygral expansion is not sufficient even by these treatment methods, in which there has been a room to make improvement yet.
As a method for improving such a point, a method for stabilizing the hygral expansion behavior of high grade woolen fabric has been proposed in which ethylene glycol diglycidyl ether (hereinafter referred to as EGDE) or propylene glycol diglycidyl ether (hereinafter referred to as PGDE) is used as a main agent, and polyvalent carboxylic acid or its salt is used as a catalyst thereof (Japanese Patent Laid-open No. 55-36343).
In this stabilization method, the woolen fabric is immersed in a weakly acidic treatment solution comprising the above-mentioned EGDE or PGDE and the above-mentioned catalyst, squeezed, and preliminarily dried, followed by a heat treatment at 150.degree. C., so as to suppress the behavior in which crimping of yarn is increased or reduced depending on a degree of hygroscopic absorption or evaporation of moisture.
However, in the above-mentioned stabilization method, EGDE or PGDE is made into a water-soluble solution using a solvent of isopropyl alcohol having a solubility parameter of 1.15 (cal/cm.sup.3).sup.1/2 and a boiling point of not more than 100.degree. C., so that in the prepared treatment solution, a reaction amount with the woolen fabric is not so large, and this solvent film disappears upon a heat treatment at 150.degree. C. In addition, the polyvalent carboxylic acid or its salt (for example, monosodium citric acid salt), which is used as the catalyst for reacting the above-mentioned EGDE or PGDE with the woolen fabric, does not have a fast reaction speed, a cross-linked structure obtained by the reaction under this catalyst is poor in durability against hydrolysis, and consequently the stabilization effect on the hygral expansion has not been so high. In addition, in the case of the above-mentioned stabilization method, the emulsifying agent comprising EGDE or PGDE remains in the woolen fabric, so that there has been such an inconvenience that the water repellent performance of the woolen fabric is reduced.
An object of the present invention is to provide a method in which the hygral expansion behavior of protein fiber products is stabilized more surely without deteriorating flexible feeling.
Another object of the present invention is to provide a method for stabilizing the hygral expansion behavior in which scarcely water-soluble by-products generated by a heat treatment of protein fiber products are removed so as to make it possible to improve the quality of the protein fiber products.